The present invention relates to the means for opening an orifice provided in a receptacle intended to contain a substance capable of sdlidifying, such as a metal melt, particularly steel or cast iron.
It applies to methods for closing and opening, by means of shutters, of the above- mentioned orifice, which may be intended either for introducing material into the metal melt through the wall of the container, or for emptying the container of all or a part of its contents.
In general, the wall of the container receives an internal spout and a fixed refractory plate pierced by facing orifices, and a movable external shutter.
In the use of such external shutters, it has been found that the metal sets very quickly in the region of the piercing in the fixed refractory plate and in the casting channel of the internal spout, that is to say, when metal has spent some time in the container, the metal does not flow when the shutter is opened. The setting of the molten metal results from an excessive heat loss to which it is subjected in contact with the refractory materials forming the inner spout of the fixed plate and the movable plate of the shutter and the imposed geometry of the casting channel in this region.
Hitherto, when the above- mentioned phenomenon appeared, the procedure was to blow oxygen into the casting channel to produce a sufficient heating of the region in question to re-form the casting jet, this blowing-in being generally carried out from outside the container, the shutter being wide open.
Attempts have been made to avoid this difficulty by preventing the access of the molten metal to the casting channel before the first opening of the shutter, particularly by the introduction of a product into the casting channel before filling the container with the liquid metal. The product can be in the form of a solid, deformable or fusible plug, a liquid composition such as, for example, lead or more generally in the form of a sand, for example zircon, silica, chromite, and graphite in pure or mixed form. A feature of these proposals is that the plugging product is always supposed to flow through the casting hole when the shutter is opened, which can moreover present some disadvantages.
It is found in practice that these processes do not make it possible to guarantee completely that metal will flow after the shutter is opened. Whatever the product employed, a solidified bridge is sometimes formed which is sufficiently strong to hold up the liquid metal. For this reason, the initial solution, consisting in blowing in oxygen through the casting channel, is being used again. In addition to the particular disadvantages of this process, it happens that, in some cases, the design of the casting device makes access to the casting hole difficult or even impossible. This is the case, in particular, when the spout is extended by a long tube intended fdr the protection of the metal jet, or when the casting is carried out under vacuum. A more recent invention, described particularly in the patent applied for in Switzerland on July 12, 1968 under No. 10,437/68, proposes to avoid or eliminate the above- mentioned setting of the molten metal in the casting channel by blowing in gas under pressure in the lower part of the said casting channel. The introduction of the gas is obtained particularly by means of a gas supply opening into at least one additional hole in the movable shutting plate of the shutter, the said hole being capable of being shut or not by a refractory substance permeable to the gases and impermeable to the metal, at least when the gas is allowed to pass through the said substance.
Such a process is found in practice to guarantee a satisfactory percentage of opening but nevertheless has some disadvantages.
Experience shows, in fact, that a permanent circulation of gas in the casting channel does not necessarily guarantee the total absence of solidifying of the metal.
The gas can in fact continue to pass through one or more channels within a plug of metal which is solidifying.
When the introduction of gas is stopped and the intention is to carry out the casting by sliding the movable plate into an appropriate position, the said channels block instantly and the plug of solidified steel becomes consistent enough to prevent the casting of the hot metal contained in the receptacle.